The present invention relates to rotary shutters. In particular, the present invention relates to a high-speed rotary shutter for a camera.
A camera generally consists of a housing containing a light-sensitive film, a lens system, a shutter system and a film advance mechanism. Before an object is exposed on the light sensitive film, the film exposure area, shutter and lens are all in optical alignment along an optical path. When the camera is activated, the shutter is opened enabling a completed optical path between the object and the exposure area on the light sensitive film. After exposure, the shutter closes and the film is advanced. In some instances, a mirror moves in and out of the optical path to selectively direct an image to a viewing screen and to move out of the exposure path during film exposure.
A camera shutter functions to admit light rays to the film for a controlled--and usually very brief--period of time, momentarily exposing the object on the film. Shutter opening time may be varied, depending on the amount of exposure desired.
Two types of shutters commonly used in the camera industry are leaf shutters and focal plane shutters. Leaf shutters include a number of thin steel plates, known as shutter leaves, which rotate about pivot points in such a way that when they are rotated outward they admit light rays to the film, and when they are rotated inward, the shutter is closed blocking light rays to the film. Leaf shutters have an relatively high shutter speed and have the ability to be synchronized with the camera flash. Due to the number of moving parts, leaf shutters are inherently maintenance prone.
Focal plane shutters include two roller blinds which move in the same set of tracks. Upon activation, the first blind, covering the film, is rolled across the film onto a spool. Next, the second blind rolls across the film at the same speed and covers the film again. Together the two blinds form a slit which travels across the film gate. For long exposure times, the second blind waits a relatively long time before following the first blind. For short exposures the second blind will quickly follow the first, resulting in a very narrow moving slit. Focal plane shutters operate at higher speeds than leaf shutters. Similar to leaf shutters, focal plan shutters are high maintenance shutters, requiring regular cleaning, maintenance, and lubrication.
Commercial photography often requires taking hundreds of pictures a day, making it necessary to use highly reliable cameras. Additionally, the photos are taken in various ambient light environments which require very fast shutter speeds. Often, conditions require that the camera shutter speed must be as short as possible, but still be able to strobe synchronize with the camera flash to compensate for various deficient ambient light environments.
Rotary shutters have been developed for exposing an area of film at high speeds. These shutters are well known for their use in the motion picture industry. Typically, a motion picture camera uses a continuously revolving shutter having a slit. The film is exposed on each revolution as the slit crosses the film exposure area. Upon each slit revolution, the film is advanced to a new exposure area before the slit crosses the film exposure area again, avoiding multiple exposures or blurring.
Lyle, U.S. Pat. No. 3,504,612, suggests a high-speed shutter. The Lyle device includes a rotary shutter with a slit for quickly exposing a large area of film through the slit, and then keeping the opening closed as the rotary shutter revolves and the film is advanced. The high-speed shutter includes a number of cams and gears, wherein a cam follower opens a slit cover on the rotary shutter on every fourth rotation of the cam wheel. The number of exposures and exposure time may vary, being dependent upon the speed of the cam wheel and ratio between the gears driving the cam-wheels.
Park, U.S. Pat. No. 3,735,687, suggests a rotary shutter. The Park rotary shutter includes a number of disks having openings, the disks being rotated at different speeds. The disk openings become aligned with the camera aperture on multiple revolutions of the disks for operation of the camera at slower speeds.